Tungsten materials and a method for providing such materials

ABSTRACT

A METHOD FOR SHAPING AND FORMING METALLIC TUNGSTEN BY COATING TUNGSTEN PARTICLES WITH A MINOR AMOUNT OF METALLIC RHENIUM AND THEREAFTER COMPACTING AND PARTIALLY SINTERING SAID COATED PARTICLES. A METHOD FOR PROVIDING INTRICATE SHAPES OF HIGH TEMPERATURE RESISTANT, NON-DUCTILE TUNGSTEN BY RE-SINTERING SAID COMPACTED AND SINTERED RHENIUM COATED TUNGSTEN PARTICLES AT A TEMPERATURE SUFFICIENT TO DIFFUSE THE METALLIC RHENIUM INTO THE TUNGSTEN. A DUCTILE, READILY FORMABLE TUNGSTEN MASS AND A NON-DUCTILE, HIGHLY TEMPERATURE RESISTANT, TUNGSTEN MASS PROVIDED BY THE FOREGOING METHODS.

Patented May 4, 1971 3,577,227 TUNGSTEN MATERIALS AND A METHOD FOR PROVIDING SUCH MATERIALS Gail F. Davies, Mentor, Ohio, assignor to the United States of America as represented by the Secretary of the Navy No Drawing. Filed Oct. 4, 1968, Ser. No. 766,038 Int. Cl. C22c 15/00 US. Cl. 29182 2 Claims ABSTRACT OF THE DISCLOSURE A method for shaping and forming metallic tungsten by coating tungsten particles with a minor amount of metallic rhenium and thereafter compacting and partially sintering said coated particles. A method for providing intricate shapes of high temperature resistant, non-ductile tungsten by re-sintering said compacted and sintered rhenium coated tungsten particles at a temperature sufficient to diffuse the metallic rhenium into the tungsten. A ductile, readily formable tungsten mass and a non-ductile, highly temperature resistant, tungsten mass provided by the foregoing methods.

BACKGROUND OF THE INVENTION This invention relates generally to ductile tungsten sheet materials and more particularly to a method for forming tungsten sheet into intricate shapes without losing its good thermal resistant characteristics.

Although tungsten metal has long been desired for its high thermal resistance, high erosion resistant and good electrical properties, its relatively low ductility and high brittleness has severely limited its range of applications to those uses in which sheet rolling or shaping into intricate forms are not required. While the prior art teaches that a pure, high density form of tungsten sheet can be obtained by a severe cold working process, the end result of such a process is a very fine grained and brittle material not generally suitable for most practical uses. To overcome this problem, the art has sought to alloy tungsten with more ductile metals such as rhenium, nickel or lead in hopes of obtaining a compromise between the good thermal properties of tungsten and the formability of the alloying metal. Unfortunately, adequate ductility is obtainable by this technique only if amounts of at least 5% by weight of the alloying metal is used; an amount which tends to destroy the thermal resistance of the tungsten to below tolerable levels. Thus, while tungsten alloying does enable the formation of a highly ductile and formable material, the desirable high thermal resistance of the pure tungsten is lost.

It would obviously be desirable to provide a method whereby tungsten may be readily converted into any desired shape without significantly sacrificing its high thermal resistance or other good thermal properties.

It would further be desirable, for certain high temperature operations, to provide a method whereby tungsten can be formed into a high temperature resistant porous body. A porous body could find particular utility in the aerospace technology as hot gas spargers or transpirationcooled rocket nozzles by passing gases passed through the pores of the metal. A porous tungsten product could also be especially useful in the rocket and missile technologies as an erosion resistant overlay for phenolic cones. The prior art techniques for forming tungsten, however, are generally inadequate for providing the intricate shapes, the critical porosity and the low density necessary for such applications.

It would therefore be further desirable to provide a method for forming ductile low density and high porosity,

tungsten sheets, a combination not heretofore available in the art.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide a method whereby tungsten may be readily formed and shaped without sacrificing its high thermal resistance or other good thermal properties.

It is a further object of this invention to provide a method for forming ductile tungsten sheet of low density and high porosity which can be shaped and then re-converted into a high ductile, high thermal resistant form.

It is also an object of tis invention to provide a novel ductile tungsten mass of either high or low porosity which can be readily formed into intricately shaped objects.

It is also an object to provide a novel high temperature resistant, relatively non-ductile tungsten mass adaptable for aerospace applications.

These and other objects are accomplished herein by the process of coating tungsten particles with a minor amount of metallic rhenium (bright), compacting and sintering the rhenium coated tungsten particles so as to fuse the rhenium coatings into a formable coherent ductile mass, shaping the ductile mass and then sintering the shaped mass at temperatures sufficient to ditfuse the rhenium coating into the tungsten particles thereby providing a high temperature resistant rigid, non-ductile tungsten body.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT According to the method of this invention, tungsten particles are coated with discrete amounts of rhenium by any of the state of the art techniques such as electroplating, electroless plating, vapor deposition or vapor coating. Depending on the size of the tungsten particles, the rhenium coating thickness may range from about 0.1 mils to about 2.0 mils. Greater or smaller amounts may be used depending on the intended application. Normally, the weight percent of the rhenium to tungsten should be in the vicinity of about 0.5% to about 5%. Although larger percentages of rhenium may be used, they should normally be avoided since the quantity of rhenium diffusing into the tungsten on the final sintering step may be so great as to cause the temperature resistance of the tungsten product to be subtsantially impaired. Lesser amounts of rhenium may also be used but the ductility of the formable product might be undesirably low thereby preventing ready conversion into more intricate shapes. For best results, the weight percentage of rhenium should be about 0.5% to about 2.0%.

The particle size of the coated tungsten is not critical and good results are obtainable with particle size ranging from one to ten microns. Good results have been also obtained with pre-shaped tungsten masses, such as tungsten wire one eighth inch long 5 to 10 mils in diameter.

The rhenium coated particles are then cold compacted using standard power metal techniques at pressures sufficient to provide a porous plate. After compacting, the material is sintered at temperatures of between 900 C. and 1200 C. to fuse the rhenium coating and to provide rhenium to rhenium contacts between the tungsten particles. No appreciable dilfusion of the rhenium into the tungsten takes place during this initial sintering.

The intra-particle contacts within the mass, following the first sintering step, are essentially pure, highly ductile, metallic rhenium. The mass can now be easily shaped and formed, such as by hot-forming, along these ductile joints. After the desired shape is obtained, the material is resintered at a temperature of between 1400 C. and 2000 C. which is sutficient to substantially diffuse the rhenium into the pure tungsten thereby replacing the rheniumrhenium contacts with tungsten-tungsten contacts and providing an intricately shaped porous body having high temperature resistance.

Since tungsten is highly reactive with oxygen, it is desirable that each of the sintering operations be conducted in a hydrogen or an inert gaseous atmosphere so as not to cause contamination of the metals. The ultimate porosity of the product is directly dependent upon the extent of the initial compacting, and the density of the sintered mass may range from about 35% to nearly a 100% of the possible density of a pure tungsten-rhenium alloy. By this technique the tungsten may be shaped by being deformed along the highly ductile rhenium interparticle boundaries. Once the desired shape is obtained, the rhenium is dilfused into the tungsten, thereby forming a homogeneous mixture. The low temperature resistant highly ductile rhenium interparticle contacts are thereby replaced with very high temperature resistant, essentially pure, tungsten contacts.

EXAMPLE I As an example of a method of preparation, to mil tungsten wires are coated with rhenium to a thickness of 0.1 to 1.0 mil using electroplate, electroless, vapor deposition, or chemical reduction methods. The wires are then cut to lengths w to inch long and compacted using standard powder metal techniques at pressures from 10 to 50 p.s.i. dependent on the degree of porosity desired. After compacting to a sheet the material is sintered in dry hydrogen for 1 hour at 1000-1200 C. to diffuse the rhenium to rhenium surfaces of each wire into a contiguous section.

The material is then formed to the desired shape, cold or warm depending on the severity of the required deformation, after which it is further sintered at 2000 C. for 1 hour in dry hydrogen to dilfuse the rhenium completely in the tungsten.

EXAMPLE H Tungsten particles varying from 1 micron to 200 microns are coated with rhenium using electroplate, electro less, vapor deposition or chemical reduction methods, to provide a discrete coating of rhenium metal (bright) on each tungsten particle. This coating may range from 0.1 to 2.0 mils thick dependent on the tungsten particle size employed. The coated powder as produced is then hot-pressed in hydrogen at 10001200 C. and under pressure adequate for compaction in the fixed closure die. Density is determined by the amount of material and the volume of the die in the closed position. Time to sinter is generally related to thermal capacity of the furnace with dwell at maximum temperature being limited to 10 minutes.

After compacting, the material is subjected to the desired forming operation and subsequently re-sintered in dry hydrogen, vacuum, or inert gas for 1-3 hours at 18002000 C.

EXAMPLE III Tungsten powder of selected particle size as dictated by the desired pore size and permeability is precoated with rhenium to a thickness of 0.1 to 1.0 mil. The powder material is then loaded in a gas-tight stainless steel sheath provided with an anti-bond coating after which it is evacuated and sealed. The sheath is then heated to 1000 C. and hot-rolled to a predetermined density ranging from 45 percent to maximum possible. At this point it is formed and then resintered at 2000 C. to fully difluse the rhenium in the tungsten.

EXAMPLE IV Using powder as described in Example III, the material is fed into a powder-rolling device at a temperature of 600800 F. where it is compacted to a porous sheet. The rolled sheet is then sintered at 1000 C. for 30 minutes, after which it is formed to the desired shape. After forming, it is fully sintered at 18002000 C., diffusing the rhenium in the tungsten and rigidizing the refractory body.

While the invention has been described and illustrated in connection with certain preferred embodiments, it will be clearly understood that many modifications may be made by those skilled in the art Without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A method for forming .a rigid non-ductile tungsten mass which comprises:

(a) coating tungsten particles with a minor amount of metallic rhenium,

(b) compacting and sintering said rhenium coated tungsten particles at a temperature between about 900 C. and about 1200 C. so as to diffuse the rhenium to rhenium surfaces and to form a coherent ductile mass,

(c) forming said coherent ductile mass into a desired shape, and

(cl) resintering the product of step (c) at a temperature between about 1400 C. and about 2000" C. so as to diffuse said rhenium into said tungsten particles and to provide a rigid, non-ductile tungsten mass.

2. A rigid porous non-ductile tungsten mass formed by the process of claim 1.

References Cited UNITED STATES PATENTS 3,236,699 2/1966 Pugh 207X 3,300,285 1/1967 Pugh 75-207X 3,375,109 3/1968 Peters 75-212 3,399,981 9/ 1968 Maykuth 29-1822 OTHER REFERENCES Goetzel, Treatise on Powder Metallurgy, vol. 1, pp. 673-675, 1948, Intersc'ience Publishing, N.Y. I

BENJAMIN R. PADGETI, Primary Examiner B. H. HUNT, Assistant Examiner US. Cl. x12, 75-176, 212, 214, 2g; 

